Ignition switch circuit on bikes

[His Dudeness]

If you look on the wiring diagram for the Fazer and for most bikes from what I can see the main power wire runs from the battery, through the main fuse then to the ignition switch, then from the ignition switch to the fuse box and from the fuse box it runs to all the other circuits through the various fuses. That means the ignition switch and the connectors and wiring to it have to take the full switched current for the whole bike. If you have a fault on that circuit like the common burnt connector going to the ignition caused by a poor connection in the connector or high resistance in the ignition switch from old age and wear and tear, the voltage to everything drops including the ignition coils so you would have weaker spark. So the question is why do they design it like that where the ignition switches all the current? Would it not make more sense if the ignition switched a relay and the relay powered the fuse box? That way the ignition switch only passes a tiny current or is there a reason why they use the ignition switch to switch the current and they don't use a relay?

[Fazerider]

Well I guess there’s no reason the contacts in an ignition switch can’t be made as robust as those in a relay, but I take your point that it’s a long and complicated path.
The headlights would be the main area where a relay would be of benefit as they take enough current for the resistance of the wiring to lose a significant voltage (though running the bulbs with a volt more will reduce their life by a factor of about 4).

[limax2]

On the 2002/3 Foxeye FZS600, and presumably on the 1,000, the headlights are indeed controlled by a couple of relays. When I fitted a Foxeye fairing and lights with twin main beam and twin dip to a 1998 FZS600 I had to do a bit of head scratching because the earlier wiring harness didn't lend itself to taking the set-up and relays from the 2002/3 model.
Instead i came up with the layout shown in the (poor quality) picture here which uses a couple of bog standard relays. As anyone with a Boxeye knows those lights are very poor so now ten times better.
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[TOM VR46]

Thank you for diagram layout . Ive been trying this for a while as I have a headlight which I have fitted two H4 bulbs. But when it comes to auto electrics I somehow get lost :rolleyes . So it will now be 2 relays soon , and ill give this a go.
To explain how lost I get with electrics, put two LED sidelights in,,,, and they blew to bits. :'( Going to try other type of LED's and see if they work.
But will give this a try with headlighs when I get time. Ive took the time to modify the headlight to two H4, so shame not to put to full use.

[His Dudeness]

On the 2002/3 Foxeye FZS600, and presumably on the 1,000, the headlights are indeed controlled by a couple of relays. When I fitted a Foxeye fairing and lights with twin main beam and twin dip to a 1998 FZS600 I had to do a bit of head scratching because the earlier wiring harness didn't lend itself to taking the set-up and relays from the 2002/3 model.
Instead i came up with the layout shown in the (poor quality) picture here which uses a couple of bog standard relays. As anyone with a Boxeye knows those lights are very poor so now ten times better.
[smg id=3374]

Excellent drawing limax Very clear and has all the info needed. Taking the the power for headlight away from the ignition switch circuit and giving the headlight it's own circuit seems like a good idea since the headlight is probably the biggest load on the fuse box. The foxeye has relays for the headlight but it looks like the relay gets it's switched power from the fuse box so the full current still goes through the ignition switch so that's not any better than the way the boxeye does it if you're looking at it from the point of view of the load through the ignition switch. The way limax has drawn it the current for the headlights would be coming straight from the battery so his way seems better to me.

The way I was thinking to do it was you have a relay beside the fuse box. When the ignition key is switched on it switches on the control side of a relay and powers the whole fuse box. The switched power would come from the battery positive through the relay and then to the fusebox so the load is taken off the ignition switch. The battery is right beside the fuse box so the power wire would only need to be a few inches long so less voltage drop and the full current doesn't need to go through the ignition switch and the wiring to the ignition switch so less voltage drop there too. Seems like a better way to do it to me. The only reason I can think of why they don't do it that way is maybe it would make the bike easier to steal? If you bypassed the relay you would put power to the fusebox and turn everything on without the key but the bike still wouldn't start since the switched ground to the ignitor would still be open in the ignition switch so you would still have to turn the key to make the bike start.

[limax2]

Glad you both approve of the wiring diagram. It has stud the test of time and given no trouble in the few years since I did it.
For no good reason here is a photo of the bike. The one with the modified electrics is a 1998 model but fitted with the later Foxeye fairing.
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[redmandan]

2 fantastic looking bikes, i'm a little jealous.


Off topic but how'd you get on with the bubble screen on the box eye? I've read mixed reports.

[limax2]

2 fantastic looking bikes, i'm a little jealous.


Off topic but how'd you get on with the bubble screen on the box eye? I've read mixed reports.

Thanks for the complement. The photo was taken a few years ago just after i'd rebuilt the bike and done the fairing mod. They are not always as clean as that.
Personally I find the bubble screen a big improvement. With the standard screen I used to get more wind blast and buffeting onto the front of the helmet. Nothing too dramatic but a definite improvement with the taller screen. Probably not as many bugs on the visor either.

[redmandan]

It's a mod I've been itching to get. I wish I could ride more but I've become something of a 4 or 5 weekends a year kind of rider. This usually involves 3-4 hours of motorway to get to the good roads. Wind buffeting and a face full of insects make for an unpleasant experience.


Maybe this year I'll make the final click and order.